It is known that several types of disulfonate surfactants exhibit high hydrophilicity and certain types have been suggested for use in detergent formulations and enhanced oil recovery operations.
One type of disulfonate surfactant is a diphenyl ether disulfonate, which is commercially available from the Dow Chemical Company under the trademark DOWFAX.RTM.. These surfactants have the general formula: ##STR1## where R and R' are linear alkyl groups having 6 to 18 carbon atoms and each M.sup.30 is a metal cation, where one of R or R' may be absent.
DOWFAX.RTM. surfactants are manufactured by alkylation of diphenyl oxide with an olefin followed by direct sulfonation of each of the phenyl rings. The sulfonation can be carried out in an inert solvent, such as methylene chloride, using a sulfonating agent such as chlorosulfonic acid.
A second type of disulfonate is produced from an oxyalkylated alkylphenol. The general structure, which is disclosed in U.S. patent application Ser. No. 109,385 filed Oct. 15, 1987, by G. F. Teletzke et al., is shown below. ##STR2## where R is a linear or branched chain alkyl group with n carbon wherein n ranges from about 4 to about 30;
x ranges from 0 to about 20 and y ranges from 1 to about 50; PA1 R' is a linear or branched chain alkyl group with m carbon atoms wherein m ranges from 1 to 4; and PA1 each M.sup.+ is a cation. PA1 R', R" and R'" are independently H or C.sub.1-3 alkyl groups; PA1 x ranges from 0 to about 10; PA1 y ranges from 0 to about 50; and PA1 each M.sup.+ is a suitable cation. PA1 The dianion is then reacted with an aqueous sulfite solution to displace the sulfate and replace it with a sulfonate. The structure of the disulfonate (APDS) is: ##STR4## where the structural parameters are defined above. PA1 R', R" and R'" are independently H or C.sub.1-3 alkyl groups; PA1 x ranges from 0 to about 10; PA1 y ranges from 0 to about 50; and PA1 each M.sup.30 is a suitable cation comprising ammonia, amines, ethanolamines and metal mono- or di-cations. PA1 R' and R" are the same as defined above. PA1 R', R" and R'" are independently H or C.sub.1-3 alkyl groups; PA1 x ranges from 0 to about 10; and PA1 y ranges from 0 to about 50. PA1 R', R" and R'" are independently H or C.sub.1-3 alkyl groups; PA1 x ranges from 0 to about 10; PA1 y ranges from 0 to about 50; and PA1 each M.sup.+ is a suitable cation comprising ammonia, amines, ethanolamines and metal mono- or di-cations.
The structure of this disulfonate is significantly different from that of the DOWFAX.RTM. surfactants. For example, the surfactants of formula II contain an oxyalkyl chain that can be composed of repeating units of C.sub.2 to C.sub.5 alkenyl oxides (for example, ethylene oxide). Another major difference is that one of the sulfonate groups is attached at the terminal end of the oxyalkyl chain. The second sulfonate group is attached to the phenyl ring.
The oxyalkyl chain of formula II surfactants imparts hydrophilic or lipophilic properties that are not found in the DOWFAX.RTM. surfactants. In addition, two or more alkenyl oxides can be incorporated into the oxyalkyl chain to provide structural combinations that provide a range of surfactant properties.
Previously proposed methods for preparing formula II surfactants have inherent drawbacks. One process involves the alkylation of phenol or methyl phenol followed by oxyalkylation. Propane sultone is then added to the terminus of the intermediate oxyalkyl alkyl phenol. This process requires the presence of a strong base, such as sodium metal or caustic, in an anhydrous aprotic solvent in order to get high yields of the monosulfonate. The monosulfonate is then reacted with chlorosulfonic acid, or other suitable sulfonating agent to add a sulfonate group to the phenyl ring. Under strong acid conditions the propanesulfonate group is easily removed, limiting the yield of the disulfonate. In addition, propane sultone is an expensive and hazardous reagent. This synthesis route cannot be adopted readily to a low-cost commercial process to manufacture APDS.
Another method of synthesizing formula II surfactants involves the use of allyl chloride adducts. In this procedure, allyl chloride is reacted with the terminus of the oxyalkyl chain in the presence of a strong base using an anhydrous aprotic solvent to form an allyl ether. The allyl ether is then reacted with chlorosulfonic acid, or some other suitable sulfonating agent, to add a sulfonate group to the phenyl ring. The final step is to form the second sulfonate group by addition of sodium bisulfite to the terminal olefin in an aqueous sulfite solution. This method is also comparatively expensive and disulfonate yields are low.
Still another method of synthesizing formula II surfactants involves converting the terminal hydroxyl group in the oxyalkyl alkylphenol chain to a chloride, sulfonating the phenol ring followed by displacing the chloride by sodium sulfite (Strecker reaction) in aqueous sodium sulfite. The limitations of this route are identical to those in the two methods mentioned above.
High disulfonate yields are important for many end uses of the disulfonate. Often with previously suggested synthesis routes, a large fraction of the product will have only one sulfonate group. Disulfonates containing a large fraction of monosulfonate would be undesirable for many applications that require a highly hydrophilic surfactant.
Moreover, methods suggested in the past for synthesizing ADPS will be inherently costly, involving expensive raw materials and processing.